All black & white films and most color films used a silver based soundtrack. Some color processes used cyan dye based soundtracks that yielded a generally inferior sound quality in addition to being detected by the projector's sound reader as being of lower volume than a silver track. The dye based track was less costly because it was printed at the time that the picture was printed to the film. Silver tracks required several additional steps in order to create a small band of black & white film along the picture edge upon which the sound image was photographically printed. Believe it or not, dye based soundtracks are being forced upon the theatre industry once again. This time the excuse is "environmental reasons". Exactly why the soundtrack in the Cinecolor example at bottom left is green remains a mystery to the Curator.